A public inquiry into the death of poisoned spy Alexander Litvinenko has been formally opened in London.

Coroner Sir Robert Owen suspended the current inquest into Mr Litvinenko's death before opening the inquiry, which was announced by Home Secretary Theresa May last week.

It will allow investigators to probe whether Moscow was behind the former KGB officer's murder and comes at a time of worsening relations between the UK and Russia.

Mr Litvinenko was poisoned with radioactive polonium-210 while drinking tea with two Russian men, one a former KGB officer, at the Millennium Hotel in London's Grosvenor Square.

His family believes he was working for MI6 at the time and was killed on the orders of the Kremlin.

Former KGB bodyguard Andrei Lugovoi and Dmitri Kovtun have been identified as suspects, but both deny any involvement and remain in Russia.

Opening the public inquiry, Sir Robert said the Crown Prosecution Service (CPS) wanted to prosecute the pair for murder, but extradition was refused by Moscow.

Video:Litvinenko Death An 'Accident'

He said there is a "prima facie case" that the Russian state was responsible for Mr Litvinenko's death.

Secret government documents relating to the case will not be heard in public during the inquiry, which is due to start in January and may last a year.

The Government previously resisted launching a public inquiry, and instead said it would "wait and see" what a judge-led inquest found.

Video:Lugovoi Ends Litvinenko Assistance

But Mr Litvinenko's widow, Marina, challenged this and the High Court said the Home Secretary must reconsider her decision.

Ms Litvinenko told Sky News she hopes the public inquiry will find out the truth to her husband's murder.

"I think the coroner will do the right decision in the end," she said.

Video:London 'Hotspot Of Espionage'

Ministers had been under pressure to hold a public inquiry since last year when Sir Robert said he could not hold a "fair and fearless" investigation with an inquest.

The aim of the inquiry is "to conduct an investigation into the death of Alexander Litvinenko in order to ascertain who the deceased was; how, when and where he came by his death; identify where responsibility for the death lies and make appropriate recommendations".